1. Field of the Invention
The present invention relates to suspension systems for wheeled motor vehicles and, more specifically to a suspension system incorporating new and improved control rod linkage configurations.
2. Discussion
The present invention finds particular utility in the heavy duty truck and trailer industry. In this industry, the use of air suspension systems has become quite popular due to their softer ride characteristics. In these suspensions, equivalents of air springs, such as hydraulic cylinders with accumulators, are sometimes alternatively used. Air suspension systems in common use typically utilize trailing arms, also called main support members, that are rigidly attached to the vehicle axles to support the vehicle frames upon the vehicle wheels. The trailing arms are pivotally attached at one end to the vehicle frames with air springs mounted between the frames and the other end of the trailing arms.
The trailing arms may take the form of gooseneck shaped Z-springs. U.S. Pat. Nos. 4,693,486, 3,547,215, 4,858,949 and 5,346,247 provide examples of such trailing arm suspensions. Alternatively, in some common designs, the trailing arm may take the form of a straight leaf spring.
Z-springs add a significant amount of weight to trailing arm air suspensions. The Z-springs typically weigh around 60 lbs. each. Additionally, the relatively large amount of material that goes into manufacturing the Z-springs is costly and the size of the Z-springs take up a substantial amount of space underneath the vehicle. Use of Z-springs may also require the use of additional associated components which adds even more weight.
The suspension frequency of a suspension system has an impact upon the ride quality of the truck. A suspension with a high suspension frequency is by its nature more rigid and thus transmits to the frame inputs such as road irregularities. The high rigidity of such a suspension also means that the motion of the suspension components in response to inputs is minimal. Movement of the suspension components isolates the energy resulting from the road inputs. The more the suspension components move in reaction to an input, the more energy is isolated or dissipated. The excess energy that the high frequency suspension doesn't isolate or dissipate is transmitted to the truck body and shows up as vibration and a rough ride quality. In contrast, a lower frequency suspension has components that move more freely when subjected to inputs. This isolates or dissipates more energy and thus produces less vibration and a smoother ride.
Trailing arm suspensions, such as the one shown in FIG. 1, are torque reactive. Due to the uses of higher horsepower engines and advances in engine technology, there have been increases in the torque output of heavy duty truck engines. Such increases have exacerbated the problems of driveline vibration and wheel hop associated with the torque reactive trailing arm suspensions. When increased torque is applied to the drive train of a truck equipped with such a torque reactive suspension, such as during acceleration, the frame of the truck rises up and away from the drive axle. This condition is known in the art as "frame rise" and results in the driveline vibration and wheel hop.
Trailing arm suspensions clamped rigidly to the axle tend to twist the axle housing in reaction to road surface irregularities encountered on one side of the vehicle during operation. This axle twist tends to lift the tires on the opposite side of the vehicle off of the ground, sometimes to the point where traction is lost.
Axle twist is also detrimental to the fatigue life of the axle. As a result, several truck and trailer manufacturers require heavier axle wall housings for use with trailing arm air suspensions which increases the axle weight.
It is therefore an object of the present invention to provide an air or hydraulic suspension system that saves weight and space and reduces cost through the elimination of Z-springs and similar trailing arms and associated components.
Another object of the present invention is to provide an air or hydraulic suspension that has a low suspension frequency.
Yet another object of the invention is to provide a suspension that maintains greater tire traction when road surface irregularities are encountered.
Yet another object of the invention is to improve the axle connection and thus enhance axle fatigue life.